1. Field of the Invention
This invention relates to an etalon which is disposed in a laser resonator to make the laser oscillate in a single longitudinal mode and a laser which oscillates in a single longitudinal mode by virtue of the etalon.
2. Description of the Related Art
There has been known a solid state laser in which a solid state laser rod doped with a rare earth metal such as neodymium is pumped with a laser beam emitted from a semiconductor laser (laser diode).
In such a laser, it has been put into practice to dispose an etalon in the resonator as a wavelength selector in order to suppress generation of mode competition noise, thereby making the oscillation mode of the laser a single longitudinal mode. See, for instance, "Optics Letters, Vol.18 (1993) p.420".
However in a laser in which an etalon is disposed in the resonator in order to obtain a single longitudinal mode oscillation, there has been a problem that the output of the laser greatly fluctuates due to change in the environmental moisture and/or aging of the laser.